1. Field of the Invention
This invention relates to an apparatus and method for introducing fastener collars into tubular magazines associated with fastener installation machines which feed the collars onto the exposed ends of fastener pins. A series of collars strung on a flexible mandrel is inserted within a tubular magazine and released from the mandrel thereby loading the magazine.
2. Description of Prior Developments
Fasteners of the pin and collar variety are used in aircraft construction for fastening panels to frames, e.g. to form aircraft wings and aircraft fuselages. Each fastener or lockbolt includes a pin having a head and shank portion extendable through aligned circular openings in the workpieces that are to be fastened together. A cylindrical collar is placed on the exposed shank portion of the pin, after which a fastener-setting tool is operated to swage the collar into and around grooves formed in the shank portion of the pin.
The present invention is concerned with devices for placing the cylindrical collars on shank portions of the lockbolt pins prior to the fastener-setting operation. Existing collar-feeding devices are supplied with collars through flexible tubular magazines that are pre-loaded with collars which are arranged serially in end-to-end relation. A pressure source associated with the collar-feeding device forces the collars out of the tubular magazine and into the collar-feeding device as required to locate each collar in position for feeding onto a fastener pin.
The tubular magazines are configured as elongated flexible tubes, each about twelve feet long. Each fastener has a diameter varying from about one fourth inch to about one half inch depending on the size of the associated lockbolt. Each collar has an axial length that approximates the collar diameter. It can be seen that each tubular magazine will contain a fairly large number of fastener collars, e.g. several hundred or more collars arranged end-to-end within the magazine.
Each tubular magazine is typically loaded with collars by an operator of a fastener installation machine at an installation site by temporarily attaching one end of the magazine to a vibratory bowl apparatus containing large numbers of fastener collars. Vibratory motion of the bowl causes the fastener collars to move in a circular fashion around the bowl periphery and upwardly along a curved ramp leading to a vertical chute. An optional collar orientation device may be provided at the end of the ramp to axially orient assymetrically shaped collars prior to their entry into the vertical chute. The collars migrate into the chute, where they drop into the tubular magazine that extends downwardly from the chute. The remote end of the tubular magazine is connected to a vacuum source, such that a vacuum force is applied to the collars to draw them along the tubular magazine so as to substantially fill the magazine along its entire length.
One drawback to this method of on site loading of the magazines with collars is that the one or more vibratory bowls are typically required at each installation site. These magazine loading machines not only require significant floor space but are also quite expensive. Moreover, the vibratory bowls and associated collar feeding apparatus require significant maintenance and are prone to malfunction and breakdowns which necessitate immediate attention and repair.
Another drawback associated with the existing method of filling the tubular magazines with fastener collars at an end-user installation site is that dirt, metal chips and other debris can be drawn into the magazine from the vibratory bowl along with the fastener collars. Also, the fastener collars will sometimes be accompanied by slugs of metal produced during the collar manufacturing operation. These slugs are cylindrical plug-like elements that are punched out of the collar material to form the annular collar configuration. Occasionally a slug will remain loosely attached to a formed collar, or a detached slug may be mixed in with collars received from the collar-manufacturing facility. Should slugs or other contaminants get into the magazine, the collar feeding device can become jammed, malfunction and/or cause damage to the workpieces being fastened.
Another problem related with loading collars within a collar storing and feeding magazine is that sometimes collars of one diameter will inadvertently become mixed in the vibratory bowls with collars of a different diameter. As a result, collars of a relatively small diameter can be introduced into magazines containing larger diameter collars. When the collar feed device attempts to feed the small diameter collar onto a large diameter lockbolt pin the feed mechanism can jam or otherwise malfunction thereby necessitating a rework of the workpieces being fastened. The same situation can develop if assymmetrical or "beaded" type collars are being fed if one or more collars are incorrectly axially inverted or loaded "upside down" in the magazine. In some cases, the collars can be incorrectly loaded sideways, or rotated 90.degree. from their correct or desired orientation. This is particularly the case with axially short length collars.
Still another problem associated with current collar loading techniques is the loss of a wax-like lubricant coating from the surfaces of the collars as the collars impact against one another in the vibratory bowls. Lubricant can also become ineffective if exposed to the ambient for extended periods of time. Once the lubricant is lost or degraded, the collars resist removal from the installation tooling after being swaged over a fastener pin. This condition can cause the installation tooling to jam.
When the collar outer surface is bare, i.e. non-lubricated, the swaging die encounters increased resistance which leads to increased stress on the die and elevated ejection forces required to separate the swaging die from the collar after the fastener-setting operation. The service life of the swaging die may be adversely affected by the absence of a lubricant film on the collar outer surface.
With existing procedures, lubricant film is applied to each collar before it is introduced into the vibratory bowl apparatus used to feed collars into the tubular magazine. The vibratory action of the bowl causes the collars to repeatedly rub against one another, so that the lubricant film is, to a large extent, rubbed off the collar surface. This loose lubricant has in the past contaminated the surfaces of the vibratory bowl and sorting and feed apparatus thereby necessitating maintenance and repair.